In recovering exhaust heat from internal-combustion engines mounted on vehicles such as passenger cars, buses, and trucks, and recovering exhaust heat from factories, stirling engines have recently been drawing increasing attention for their excellent theoretical thermal efficiency. Stirling engines can be expected to achieve not only high thermal efficiency but also energy saving, as stirling engines are external-combustion engines that heat working fluids from outside and can utilize various kinds of low-temperature-difference alternative energies such as solar heat, geothermal heat, and exhaust heat, regardless of heat sources. Patent Documents 1 and 2 disclose techniques that can be considered relevant to the present invention, as those techniques relate to heat exchangers for stirling engines and more particularly, to heat exchangers including tubes.